Electromagnetic starting switch

ABSTRACT

A starting switch for a single-phase induction motor has an armature rotatable by an electromagnet to close two pairs of electrical contacts connectable to the starting winding of the motor. The armature is balanced about its axis of rotation.

United States Patent 5 w: 3,593,233

[72] Inventor References Cited 2' I Appl- No 843.647 UNITED STATESPATENTS [22] Filed July 22,1969 2.629.031 2/1953 Ballman 335/276 45patemed J 13 197| 3,147,349 9/I964 We lch 335/125 [73] AssigneeEllenberger & Poensgen GmbH 3,178,532 4/1965 Smith 335/l 25 [32]Priorily g- 1968 Primary Examiner-Harold Broome g .9: 3.78 2Attorney-Richards and Geier [54] ELECTROMAGNETIC STARTING SWITCH 3Claims, 4 Drawing Figs. [52] us. 335/[25 S RAC A tar ing switch for asingle-phase induction [5 1m. flolh 51/06 motor has anvarmaturerotatable by an electromagnet to close 501 Field olSeardt 335/106, tpairs of electrical contacts connecmble to the starting I07, 124, 125,I28, I87, I92, 203, 271, 276, 279 Winding of the motor. The armature isbalanced about its axis 200 of rotation.

4 "2 K L N 2 17 i A 11' f i 17 z i 12 18 ELECTROMAGNETIC STARTINGSWITCII THIS INVENTION relates to an electromagnetic starting switch forsingle-phase induction motors.

The invention particularly relates to an electromagnetic starting switchfor single-phase induction motors of the type which has a rotatablemagnet armature on which there is disposed a movable contact and anelectromagnet which is connected in series with the main motor windingwhen the coil of the electromagnet is excited by the high startingcurrent, the contact is caused by movement of the magnet armature tobear against a countercontact connected to the starting winding. whenthe motor has started the current in the coil is reduced and the contactis opened by a return spring. Such a starting switch is described inU.S. Pat. No. 3,l92,340. In this case both the magnet armature and themagnetic core of the electromagnet are disposed in the lower part of atwo-part housing. The magnetic core consists of two L-shaped parts, ofwhich the arms extending out of the coil former are of unequal length.Because of these features the manufacture and assembly of the knownstarting switch are difficult and costly.

According to the present invention there is provided an electricalstarting switch for single phase induction motors having a main motorwinding and a starting winding, said switch including a rotatable magnetarmature with two movable contacts disposed thereon, fixedcountercontacts corresponding to said movable contacts and connectableto said starting winding, an electromagnet connectable in series withsaid main winding to rotate said armature against a return spring toclose said contacts when a starting current flows in said main winding.

In the switch of the invention therefore, the switching capacity isdivided between two contact pairs, so that the contacts take less loadand have a longer useful life. A high switching capacity is obtainedeven with high inductance. The two movable contacts are disposed oncontact springs of like construction which are secured to the twolongitudinal sides of the magnet armature, and they lie on a straightline extending through the axis of rotation of the armature.Consequently, there is a symmetrical arrangement of the contact springswhich is simple to manufacture. A further advantage is that the magnetarmature with the contact springs secured thereto is insensitive tovibration and shock, because the center of gravity of the magnetarmature lies on its axis of rotation.

For a further simplification of the manufacturing process, the magnetarmature is constructed as a stamping, and has on both longitudinalsides integral pins on to which the two contact springs, which areformed with appropriate apertures, are pushed and riveted. In addition,one pin can serve to hold one end of a return spring which tends to turnthe magnet armature into the circuit breaking position, and bearing atits other end on an adjusting screw disposed on a part fast with thehousing. The response of the starting switch is adjusted by means of theadjusting screw, which varies the return spring force.

The magnet armature can be made U-shaped, and the magnetic core disposedbetween its Uarrns be made straight. The end faces of the magnetic corecan be sectors of cylinders having axes parallel to the axis of rotationof the armature, and forming a single plane therewith, and being atequal distances therefrom. This arrangement causes the magnetic core tohave a strong attraction for the magnet armature, and the latter isfirmly held in the attracted position.

As in the known starting switch, the housing of the starting switchaccording to this invention may consist of a lower part and an upperpart. Particular advantages are obtained if the magnetic core providedwithin the magnet coil is disposed in the lower part of the housing andthe magnet armature is rotatably disposed in the upper part of thehousing. In this case, the magnetic core may be pressed into the formerof the magnet coil, and the said former may be inserted in selflockingmanner in a corresponding recess in the lower part of the housing. Themagnet armature may include a pin directed away from its U-arms, whichis rotatably mounted in a corresponding aperture in the upper part ofthe housing. Both the magnet armature and the magnetic core, with themagnet coil disposed thereon, are thus so placed in the two housingparts as to be readily observable and accessible, which facilitatesassembly. In addition, the possibility exists of employing the startingswitch as a control relay.

In order that the invention may more clearly be understood, thefollowing description is given, merely by way of example, with referenceto the accompanying drawings, in which:

FIG. I is a section of one embodiment of switch according to theinvention, and is also a section along the line 1-] of FIG.

FIG. 2 is a section along the line |l-ll of FIG. 1; FIG. 3 is the samesection as that of FIG. 2, showing the starting switch in the closedposition; and

FIG. 4 illustrates the starting switch according to FIGS. I to 3,connected into the circuit of a single-phase induction motor.

The illustrated starting switch comprises a housing which consists of alower part I and an upper part 2, these two parts being connectedtogether by two hollow rivets 3. A coil former 5 provided with a magnetcoil 4 is disposed in selfloclting manner in the lower part I of thehousing. A magnetic core 6 is pressed into the coil former 5.

The upper part 2 of the housing comprises an extension 7 formed with abore 8 in which there is pivotally mounted a cylindrical pin 9 of amagnet armature 10. The magnet arma ture 10 is stamped from a sheetmetal section and is bent in U- form. The U-arrns II of the magnetarmature I0 surround the magnetic core 6.

The two end faces 12 of the straight magnetic core 6 are in the form ofsectors of a cylinder, the axes of the cylinders being at equaldistances from and opposite sides of the axis of rotation I3 of themagnet armature I0, and being in one plane with that axis. The magnetarmature It) includes, on the two longitudinal sides of the partconnecting the two U-arms l1, rectangular pins 14, on to which twocontact springs 15 formed with appropriate apertures are pushed andriveted. The contact springs I5 are similar and are provided at theirfree ends with contacts I6 which cooperate with fixed countercontacts 17on connecting lugs 18. The center of gravity of the whole magnetannature It] lies on the axis of rotation I3, so that shocks andvibrations cannot cause it to swivel.

One pin 14 serves to hold one end of a return spring I9, which bears atits other end against an unthreaded sank 20 of an adjusting screw 21.The screw 21 is screwed into a nut 22 fixed in a recess in the upperpart 2 of the housing. Adjustment of the screw 21 varies the compressionof return spring I9, so that the response of the armature to current inthe coil 4 may be adjusted.

One end of the magnet coil 4 is connected to the connecting lug I8 andthe other end to a connecting lug 23. In FIGS. 2 and 3, there is shown afourth connecting lug 24, but this lug may be omitted. All theconnecting lugs 18, 23, 24 are disposed in self-locking manner incorresponding recesses in the lower part 1 of the housing. When theupper part of the housing has been mounted on the lower part I of thehousing, these connecting lugs 18, 23, 24 project out of the upper part2 of the housing, as shown in FIG. I. The connecting lugs 18, 23, 24 areformed as plug-in contacts at the ends projecting out of the upper part2 of the housing.

In FIG. 4, the starting switch illustrated in FIGS. 1 to 3 is denoted by25 and is connected in the circuit of a single-phase induction motor.One end of the magnet coil 4 is connected to the connecting lug 24 andto the connecting lug 18, which is connected to the phase source R. Theneutral conductor 0 is connected both to the main winding 26 and to thestarting winding 27 of a single-phase induction motor 28.

The iilustrated starting switch operates as follows:

Before the circuit of the main winding 26 of the electric motor 28 isclosed by a main switch, the starting switch is in the noncontactingposition illustrated in FIG. 2. When the main switch is closed, a largestarting current flows through the main winding 26 of the motor andthrough the magnet coil 4. This produces an intense magnetic field inthe magnetic core 6, which causes the magnet armature 10 to rotate sothat the contacts are closed, that is the position of FIG. 3. Current isthus supplied to the starting winding 27. The motor starts and as itsspeed increases, a back EMF is built up in the main winding 26, and thecurrent in the magnet coil 4 decreases. When a rated speed is reached,the magnetic field in the magnetic core 6 can no longer hold the magnetarmature 10 in the position illustrated in FIG. 3, and this magnetarmature 10 therefore returns, under the action of the return spring I9,to the position illustrated in FIG. 2, in which the circuit of thestarting winding 27 is broken.

If the end faces 12 of the magnetic core 6 have the shape describedabove, a relatively small airgap exists between the arms I] of themagnet armature l and the end faces even before the magnet armature isrotated. This causes strong attraction of the magnet armature onenergization of the magnetic core 6 so that the starting circuit iscertain to be closed in opposition to the return spring l9, to theposition shown in FIG. 3 in which the airgap 29 at its narrowest point30 is small, and the attraction is correspondingly large.

If the load on the motor is so high that the speed of rotation falls toa certain extent, the current in the magnet coil 4 is increased to suchan extent that the starting switch 25 is again closed, and the startingwinding 27 is energized to increase the motor torque.

I claim:

1. An electromagnetic starting switch for a single phase induction motorhaving a main winding, said switch comprising a housing having a lowerpart and a separate upper part, a straight magnetic core, a coil former,said core being fixed in said coil former, a magnetic coil carried bysaid coil former,

said coil being connected in series with said main winding, said lowerpart of the housing having a recess receiving said coil former, aU-shaped magnetic armature having two arms and a transverse portion androtatably mounted in said upper part of the housing, the two arms of themagnetic armature extending out of the upper part of the housing andinto the lower part of the housing, whereby when the magnetic armatureis energized the ends of said anns cover the two ends of said core witha small airgap, a pin fixed to said armature in the middle thereof andextending away from its arms, said pin being rotatably mounted in a boreof the upper part of the housing, two similar contact springs, separatemeans fixing one end of each of said contact springs to the transverseportion of the armature, said contact springs further having a free end,a separate movable contact carried by each free end, said free endsextending beyond said arms, and two counter contacts, the movablecontact of such contact spring being adapted to engage a separatecountercontact, the contact springs being bent during this engagement.

2. A switch in accordance with claim I, wherein said means consist ofpins holding said contact springs, said switch further comprising areturn spring engaging said armature and urging it to carry out a returnmovement, one of said pins engaging one end of said return spring, andan adjustable screw carried by said housing and engaging the other endof said return spring.

3. A switch in accordance with claim 2, wherein said magnetic core hastwo opposed end faces, said end faces having the shape of sectors ofcylinders the axes of which extend parallel to the axis of rotation ofthe armature and are in the same plane, said axes being equidistant fromsaid axis of rotation and being located on opposite sides thereof.

1. An electromagnetic starting switch for a single phase induction motorhaving a main winding, said switch comprising a housing having a lowerpart and a separate upper part, a straight magnetic core, a coil former,said core being fixed in said coil former, a magnetic coil carried bysaid coil former, said coil being connected in series with said mainwinding, said lower part of the housing having a recess receiving saidcoil former, a Ushaped magnetic armature having two arms and atransverse portion and rotatably mounted in said upper part of thehousing, the two arms of the magnetic armature extending out of theupper part of the housing and into the lower part of the housing,whereby when the magnetic armature is energized the ends of said armscover the two ends of said core with a small airgap, a pin fixed to saidarmature in the middle thereof and extending away from its arms, saidpin being rotatably mounted in a bore of the upper part of the housing,two similar contact springs, separate means fixing one end of each ofsaid contact springs to the transverse portion of the armature, saidcontact springs further having a free end, a separate movable contactcarried by each free end, said free ends extendIng beyond said arms, andtwo counter contacts, the movable contact of such contact spring beingadapted to engage a separate countercontact, the contact springs beingbent during this engagement.
 2. A switch in accordance with claim 1,wherein said means consist of pins holding said contact springs, saidswitch further comprising a return spring engaging said armature andurging it to carry out a return movement, one of said pins engaging oneend of said return spring, and an adjustable screw carried by saidhousing and engaging the other end of said return spring.
 3. A switch inaccordance with claim 2, wherein said magnetic core has two opposed endfaces, said end faces having the shape of sectors of cylinders the axesof which extend parallel to the axis of rotation of the armature and arein the same plane, said axes being equidistant from said axis ofrotation and being located on opposite sides thereof.